The invention relates to an automatic profiling equipment in which a stylus is moved relative to a model to follow the contour thereof, and in which a tool and a workpiece is to be machined thereby are disposed for relative movement with respect to each other in a manner coincident with the relationship between the stylus and the model to thereby automatically machine the workpiece. More particularly, the invention relates to a control system for such equipment.
The surface machining of a workpiece such as turbine blade, propeller, screw or the like which has a complex configuration and includes a three dimensional twist has heretofore utilized a manual grinding or polishing operation subsequent to an electrolytic machining or copy milling of a forged workpiece. Either electrolytic machining or copy milling alone cannot provide a sufficient dimensional accuracy or surface finish, while manual grinding cannot readily achieve an increased stock removal. It will be appreciated that the machining of a turbine blade, for example, by urging it against a rotating grinding wheel or a running abrasive belt while holding it with the hand of an operator requires a high degree of skill and carefulness on the part of the operator, and also involves a problem of operational safety, resulting in a very heavy work, particularly when a large size blade is to be machined. The machining must proceed while repeatedly measuring the cross-sectional gauges at a number of locations in a careful manner, thus resulting in a substantially low working efficiency. In addition, it is difficult to maintain high accuracy, and it has been impossible to avoid a reduction in the accuracy between the guages of adjacent parts.
A purely mechanical profile belt grinder using a cam is known, but requires a substantially increased machining time. Its use is limited to a turbine blade for aircraft which is of a small size and which includes a reduced twist.
A number of profile milling machines are known which have used a stylus of small radius and in which the speed control has been based on the movement of the center of the stylus. However, as the radius of the stylus increases, a proper profiling operation is prevented for certain tools which produce an amount of cutting in proportion to the time length during which the tool is held in contact with the workpiece, since the conventional control of movement has been such that the speed with which the point of contact between the model and the stylus moves along the contour of the model does not remain constant, but varies. Where the workpiece is hard and has a degree of resilience, the dimensional accuracy and/or the surface finish has been poor. With a tool such as an abrasive belt which has a relatively large width, the degree of machining depends on the angle of contact between the tool and the workpiece, and proper machining cannot be achieved for a model which has a three dimensionally curved surface, unless the tool contacts the workpiece in conformity to the configuration of the curved surface. However, no such control has been achieved in conventional profiling machines. Furthermore, the conventional profiling machines incorporated a control over a pair of orthogonal coordinates such as X and Y directions.
It is an object of the invention to provide an automatic profiling control system which assures a high machining accuracy even for an increased radius of the stylus.
It is another object of the invention to provide an automatic profiling control system which assures high machining accuracy for a tool such as an abrasive belt which has an increased width.
It is a further object of the invention to provide an automatic profiling control system capable of surface machining a workpiece such as a larged sized turbine blade of a configuration which includes a three dimensional twist.
It is an additional object of the invention to provide an automatic profiling control system which maintains high dimensional accuracy and achieves a satisfactory surface finish for a workpiece which is hard and has a degree of resilience.
It is still another object of the invention to provide an automatic profiling control system which provides control in polar coordinates rather than in orthogonal coordinates.